Nonhygroscopic, anionic pentacoordinate silicate

ABSTRACT

Nonhygroscopic, anionic pentacoordinate silicate, for example, ##STR1## soluble in commonly used organic solvents, and useful as a source of fluoride, cyanide or azide anion and as a catalyst or cocatalyst in polymerization systems, for example, the polymerization of methyl methacrylate.

DESCRIPTION

1. Field of the Invention

This invention relates to pentacoordinate silicates which serve asanhydrous anion sources and which are useful as polymerization catalystsand cocatalysts.

2. Background

Clark in Chem. Rev. 80, 429 (1980) includes in a discussion of thefluoride ion as a base in organic synthesis a review of organic andinorganic fluoride sources. Many of these have limited or no solubilityin organic solvents and are difficult or impossible to maintain in theanhydrous state because of their hygroscopic nature.

Farnham et al. in J. Am. Chem. Soc. 103, 4608 (1981) discuss structuralaspects of the anionic pentacoordinate silicon compounds of the formulae##STR2## Perrozzi et al. in J. Am. Chem. Soc. 101, 1591 (1979) disclosesimilar pentacoordinate silicon compounds of the formula ##STR3##wherein R is methyl or phenyl.

It is an object of this invention to provide an anhydrous,nonhygroscopic, thermally stable, pentacoordinate silicon compound whichcan provide a fluoride, cyanide or azide anion. Another object is toprovide such an anion source which is useful as a catalyst or cocatalystin polymerization systems. Still another object is to provide apolymerization system utilizing the aforesaid anion source. A furtherobject is to provide a process for polymerizing methyl methacrylate bymeans of the aforesaid anion source. Another object is to provide suchan anion source which is soluble in commonly used organic solvents.Other objects will become apparent hereinafter.

DISCLOSURE OF INVENTION

For further comprehension of the invention and of the objects andadvantages thereof, reference may be made to the following descriptionand to the appended claims in which the various novel features of theinvention are more particular set forth.

The invention resides in nonhygroscopic, anionic, pentacoordinatesilicates which can readily be rendered anhydrous and which areespecially suitable for use in nonaqueous solvents, particularly aspolymerization catalysts and cocatalysts for acrylate monomers,especially methyl methacrylate. More specifically, the invention residesin compounds of the formula ##STR4## wherein

R¹ and R² are both aryl or one is aryl and the other is C₁₋₄ alkyl, orR¹ and R² taken together are ##STR5##

Y is CF₃ or, when R¹ and R² are taken together, CH₃ ;

X is F, CN or N₃ when Y is CF₃ ;

X is F when Y is CH₃ ;

M.sup.⊕ is (R³)₄ N.sup.⊕, [(R⁴)₂ N]₃ S.sup.⊕ or Cs.sup.⊕ when X is F;

M.sup.⊕ is (R⁵)₄ N.sup.⊕ when X is CN;

M.sup.⊕ is [(R⁴)₂ N]₃ S.sup.⊕ or (R⁵)₄ N.sup.⊕ when X is N₃ ;

aryl is phenyl, phenyl substituted with F or C₁₋₄ alkyl, C₁₋₄ alkoxy ornaphthyl;

R³ is C₁₋₄ alkyl;

R⁴ is C₁₋₂ alkyl or (R⁴)₂ is --CH₂ --₅ ; and

R⁵ is C₂₋₄ alkyl.

The pentacoordinate silicon compounds of this invention are preparedfrom tetracoordinate silicon precursors. The latter can be prepared byknown techniques, such as the following. Hexafluorocumyl alcohol can beconverted readily to the dilithium salt, as demonstrated in theexamples, for example, by means of tetramethylethylenediamine andn-butyllithium, and then reacted with the dichlorosilane of the formulaR¹ R² SiCl₂ wherein R¹ and R² are as defined above. The reactionconveniently is carried out in a solvent, for example, tetrahydrofuran,petroleum ether, or a mixture thereof, at a temperature within the range-78° to 25° C. the tetracoordinate cyclic silane which is thus producedcan be converted to the desired pentacoordinate silicon compound bymeans of an appropriate salt which provides M.sup.⊕ and X in theaforesaid formula for the compound of the invention. For example, asdemonstrated in the examples, such moieties are provided bytris(dimethylamino)sulfonium trimethyldifluorosilicate

    [(CH.sub.3).sub.2 N].sub.3 S.sup.⊕ (CH.sub.3).sub.3 Si.sup.⊖ F.sub.2

which is known from U.S. Pat. No. 3,940,402. The reaction convenientlyis carried out at room temperature in a solvent, such as acetonitrile ortetrahydrofuran. The simplified nomenclature used in this specificationis defined by means of the formulae shown: ##STR6##1,1-diphenyl-3,3-bis[trifluoromethyl]-1,3-dihydro-2,1-benzoxasilole##STR7##1,1-diphenyl-1-fluoro-3,3-bis[trifluoromethyl]-1,3-dihydro-2,1-benzoxasilole[ion1-], tris[dimethylamino]-sulfonium salt.

The following examples demonstrate the preparation of pentacoordinatesilicates of this invention. All temperatures are in degrees Celsius.Symbols used to describe substituents are the same as those shown in theaforesaid formula.

EXAMPLE 1 A. Cyclic Silane

A solution of α,α-bis(trifluoromethyl)benzyl alcohol (C₆ H₅ --C(CF₃)₂OH: 8.76 g, 35.9 mmol) and tetramethylethylenediamine (TMEDA; 5.41 g,35.9 mmol) in petroleum ether (70 mL) was treated slowly withbutyllithium at ca. 20°. After the addition was complete, the mixturewas heated to gentle reflux for 12 h, then cooled to -25°; the resultantdianion of the formula ##STR8## was treated dropwise with a solution ofmethylphenyldichlorosilane (6.69 g, 35.9 mmol) in petroleum ether (50mL). The resultant mixture was allowed to warm to 25°, stirred for 18 h,cooled and treated with water. Ether was added and the organic layer wasseparated and washed with water, brine, dried (MgSO₄) and concentrated.Kugelrohr distillation gave a major fraction which solidified (6.44 g).Recrystallization (twice from petroleum ether) gave 4.00 g of whitesolid, mp 60°-62°. ¹⁹ F nmr: φ=-75.26 and -75.90 (A₃ B₃, J_(FF) =9.0Hz). ¹ H nmr: δ^(TMS) _(CDCl).sbsb.3 7.85-7.00 (m), 0.70 (s). ²⁹ Si nmr:+24.23 ppm. Anal. Calcd. for C₁₆ H₁₂ F₆ OSi: C, 53.04; H, 3.34. Found:C, 53.24; H, 3.31. These experimental details and the above data confirmthat the product compound is the cyclic silane of the formula ##STR9##wherein R¹ is methyl, R² is phenyl and Y is CF₃.

B. Fluorosilicate

A mixture of cyclic silane prepared as in Part A (3.94 g) andacetonitrile (20 mL) was treated with 2.89 g oftris(dimethylamino)sulfonium trimethyldifluorosilicate

    [(CH.sub.3).sub.2 N].sub.3 S.sup.⊕ (CH.sub.3).sub.3 Si.sup.⊖ F.sub.2

and stirred for 1.0 h. Volatiles were removed under a stream of nitrogenand the residue was treated with ether. The solid was filtered, washedwith ether, and dried to give 5.78 g of white crystals, mp 78°-80°(dec.). ¹ H nmr: δ^(IMS) _(CD).sbsb.3_(CN) 8.10-7.95 (m, 1H), 7.88-7.70(m, 2H), 7.58-7.00 (m, 6H), 2.72 (s, 18H), 0.14 (s, 3H). ¹⁹ F nmr:φ=-74.16 and -75.19 (A₃ B₃, J=9.5 Hz). ²⁹ Si nmr: -75.13 (s). Anal.Calcd. for C₂₂ H₃₀ N₃ F₇ OSSi: C, 48.42; H, 5.54; N, 7.70. Found: C,47.76; H, 5.49; N, 8.06. These experimental details and the above dataconfirm that the product compound is the fluorosilicate of the inventionand of the aforesaid formula wherein R¹ is methyl, R² is phenyl, X is F,Y is CF₃ and M.sup.⊕ is [(R⁴)₂ N]₃ S.sup.⊕ wherein R⁴ is methyl.

C. Cyanosilicate

A mixture of tetraethylammonium cyanide (1.16 g, 7.43 mmol) intetrahydrofuran (10 mL) was treated with a solution of cyclic silaneprepared as in Part A (2.69 g, 7.43 mmol) in tetrahydrofuran (10 mL) andstirred for 18 h under a nitrogen atmosphere. Removal of solventprovided a viscous oil which slowly solidified to a brown solid. ¹ Hnmr: δ^(TMS) _(CD).sbsb.3_(CN) 8.69-8.35 (m, 1H), 8.00-6.90 (m, 8H),3.08 (q, J=7 Hz, 8H), 1.10 (doublet of triplets, J_(HH) =7 Hz, 12H),0.63 (s, 3H). These experimental details and the above data confirm thatthe product compound is the cyanosilicate of the invention and of theaforesaid formula wherein R¹ is methyl, R² is phenyl, X is CN, Y is CF₃and M.sup.⊕ is (R⁵)₄ N.sup.⊕ wherein R⁵ is ethyl.

EXAMPLE 2 A. Cyclic Silane

The dilithium salt of α,α-bis(trifluoromethyl)-benzyl alcohol wasprepared on a 0.20 mol scale by the procedure described in Example 1A. Asolution of diphenyldichlorosilane (50.6 g, 0.20 mol) in petroleum ether(100 mL) was added dropwise to the mixture at ca. -50°. After themixture warmed to 25°, it was heated to 40° for 1.5 h. Ether (250 mL)was added and reflux was continued for 1.0 h. The cooled mixture wastreated with water, separated, and dried. Solvent was removed underreduced pressure. Petroleum ether was added and the mixture was filteredand evaporated to give an oil which was kugelrohr distilled to give 10.1g of oil, bp 140°-150° (0.2 mm). The product slowly crystallized and wasrecrystallized (hexane), mp 84°-86°. ¹ H nmr: δ^(TMS) _(CDCl).sbsb.37.90-7.15 (m). ¹⁹ F nmr: φ=-75.94 (s). These experimental details andthe above data confirm that the product compound is the cyclic silane ofthe formula shown in Example 1A wherein R¹ and R² are phenyl and Y isCF₃.

B. Fluorosilicate

A solution of cyclic silane prepared as in Part A (1.58 g) inacetonitrile (6 mL) was treated with tris(dimethylamino)sulfoniumtrimethyldifluorosilicate (1.01 g) and stirred for 1.0 h. Most of thesolvent was removed under a stream of nitrogen. Addition of ether,followed by filtration, gave 2.02 g of white crystals, mp 117°-118°. ¹ Hnmr: δ^(TMS) _(CD).sbsb.3_(CN) 8.43-8.28 (m, 1H), 8.17-7.87 (m, 4H),7.75-7.20 (m, 9H), 2.77 (s, 18H). ¹⁹ F nmr: φ=-107.3 (s, 1F), -74.1 (s,6F). Anal. Calcd. for C₂₇ H₃₂ N₃ F₇ OSSi: C, 53.36; H, 5.31; N, 6.91.Found: C, 53.14; H, 5.31; N, 6.92. These experimental details and theabove data confirm that the product compound is the fluorosilicate ofthe invention and of the aforesaid formula wherein R¹ and R² are phenyl,X is F, Y is CF₃ and M.sup.⊕ is [(R⁴)₂ N]₃ S.sup.⊕ wherein R⁴ is methyl.

C. Cyanosilicate

A solution of cyclic silane prepared as in Part A (948 mg) intetrahydrofuran (THF) (5 mL) was treated with tetraethylammonium cyanideand the mixture was stirred for 2.5 h. The solid was filtered, washedwith THF, and dried under vacuum. ¹ H nmr: δ^(TMS) _(CD).sbsb.3_(CN)8.87-8.67 (m, 1H), 8.00-7.07 (m, 13H), 3.10 (q, J=7 Hz), 1.12 (t withadditional coupling to N). ¹⁹ F nmr: φ=-74.4 (s). Anal. Calcd. for C₃₀H₃₄ N₂ F₆ OSi: C, 62.05; H, 5.90; N, 4.82. Found: C, 61.95; H, 6.25; N,5.27. These experimental details and the above data confirm that theproduct compound is the cyanosilicate of the invention and of theaforesaid formula wherein R¹ and R² are phenyl, X is CN, Y is CF₃ andM.sup.⊕ is (R⁵)₄ N.sup.⊕ wherein R⁵ is ethyl.

D. Azidosilicate

Tris(dimethylamino)sulfonium azide (245 mg, 1.19 mmol) and the cyclicsilane prepared as in Part A (500 mg, 1.19 mmol) were dissolved inacetonitrile (1.0 mL). After standing for 0.75 h the solvent was removedunder vacuum to give a white solid, mp 113°-115° (dec.). IR featured astrong band at 2050 cm⁻¹. ¹ H nmr: δ^(TMS) _(CD).sbsb.3_(CN) 8.22-8.06(m, 1H), 7.85-7.25 (m, 13H), 2.82 (s, 18H). ¹⁹ F nmr: φ=-75.0. Anal.Calcd. for C₂₇ H₃₂ N₆ F₆ OSSi: C, 51.41; H, 5.11; N, 13.32. Found: C,51.32; H, 4.95; N, 12.94. These experimental details and the above dataconfirm that the product compound is the azosilicate of the inventionand of the aforesaid formula wherein R¹ and R² are phenyl, X is N₃, Y isCF₃ and M.sup. ⊕ is [(R⁴)₂ N]₃ S.sup.⊕ wherein R⁴ is methyl.

EXAMPLE 3 A. Cyclic Silane

A solution of α,α-dimethylbenzyl alcohol (50 mmol) andtetramethylethylenediamine (100 mmol) in petroleum ether (100 mL) wastreated with butyllithium (100 mmol) at 20°, and the resulting mixturewas heated to reflux for 12 h under an atmosphere of argon. The mixturewas cooled, treated dropwise with a solution of silicon tetrachloride(25 mmol) in petroleum ether (50 mL), and stirred at 25° for 18 h. Themixture was cooled, treated with water, and extracted with ether. Theorganic layer was washed with water, dried, and evaporated. Kugelrohrdistillation provided 1.90 g of solid material which was recrystallizedfrom petroleum ether. ¹ H nmr: δ^(TMS) _(CDCl).sbsb.3 b 7.60-7.20 (m,8H), 1.68 (s, 12H). These experimental details and the above dataconfirm that the product compound is the cyclic silane of the formulashown in Example 1A wherein R¹ and R² taken together are ##STR10## and Yis CH₃.

B. Fluorosilicate

A mixture of cyclic silane prepared as in Part A (1.76 g, 6.68 mmol) andacetonitrile (10 mL) was treated with tris(dimethylamino)sulfoniumtrimethyldifluorosilicate (1.75 g, 6.36 mmol) and stirred for 0.5 h.Solvent was removed under a stream of nitrogen, and the residue wastreated with ether, filtered, and washed with ether to give a whitesolid, mp 115°-123°. ¹ H nmr: δ^(TMS) _(CD).sbsb.3_(CN) 8.00 (m, 2H),7.28-7.08 (m, 6H), 2.70 (s, 18H), 1.49 (s, 12H). ¹⁹ F nmr: φ=-115.2 (s).Anal. Calcd. for C₂₄ H₃₈ N₃ FO₂ SSi: C, 60.09; H, 7.98; N, 8.76. Found:C, 58.20; H, 7.88; N, 9.03. These experimental details and the abovedata confirm that the product compound is the fluorosilicate of theinvention and of the aforesaid formula wherein R¹ and R² taken togetherare ##STR11## X is F, Y is CH₃ and M.sup.⊕ is [(R⁴)₂ N]₃ S.sup.⊕ whereinR⁴ is methyl.

The utility of the nonhygroscopic, anionic, pentacoordinate silicates ofthis invention as polymerization catalysts is demonstrated by thefollowing experiments wherein methyl methacrylate is polymerized. Toobtain the best polymerization results, the components used for thepolymerization reactions generally should be of high purity and free ofwater and other protic materials. In the following experiments thetetrahydrofuran was distilled from sodium/benzophenone; thedimethylketene methyltrimethylsilylacetal was distilled using a spinningband column; and the methyl methacrylate was purified by passing througha column of neutral alumina.

Experiment 1

A. A solution of the fluorosilicate, in tetrahydrofuran (20 mg in 30mL), prepared as in Example 2B, at 5° C. was admixed with dimethylketenemethyltrimethylsilylacetal (0.35 mL, 2.15 mmol) and methyl methacrylate(5.00 mL, 47 mmol). The reaction mixture was allowed to warm to ca 35°C. After the exotherm had subsided and the temperature was 25° C., themixture was stirred for 3 h. Methanol was added and solvent was removedunder vacuum to yield 5.80 g of white solid polymethyl methacrylatewhich exhibited M_(w=) 2530 and M_(n) =2120 by gel permeationchromatographic (GPC) analysis.

B. A solution of methyl methacrylate (5.0 mL, 47 mmol) anddimethylketene methyltrimethylsilylacetal (0.70 mL, 4.3 mmol) intetrahydrofuran (15 mL) at 5° C. was treated with the fluorosilicateprepared as in Example 2B (35 mg). The reaction temperature was allowedto reach 60° C. The mixture was stirred at 25° C. for 1.0 h after theexotherm had subsided. Another portion of methyl methacrylate (3.0 mL)was added, and the mixture was stirred for 1.0 h after the exotherm hadsubsided. The process was repeated twice more, adding a total of 14.0 mLof methyl methacrylate. Methanol was added and solvent was removed undervacuum to yield 16.2 g of white polymethyl methacrylate which exhibitedM_(w) =3880 and M_(n) =3510 by GPC analysis.

Experiment 2

A solution of dimethylketene methyltrimethylsilylacetal intetrahydrofuran (0.70 mL, 4.3 mmol in 15 mL THF) was admixed with thecyanosilicate (38 mg) prepared as in Example 2C. Methyl methacrylate(5.00 mL, 47 mmol) was added and the mixture was stirred for 1.0 h afterthe exotherm had subsided. Another portion of methyl methacrylate (3.0mL) was added and the mixture was stirred for 18 h and then processed asin Experiment 1. The yellow solid polymethyl methacrylate which wasrecovered (9.0 g) exhibited M_(w) =2410 and M_(n) =1980 by GPC analysis.

Experiment 3

A solution of the azidosilicate, in tetrahydrofuran (50 mg in 15 mL),prepared as in Example 2D, was admixed with dimethylketenemethyltrimethylsilylacetal (0.70 mL) and methyl methacrylate (5 mL).Following the procedure described in Experiment 1, after stirring for 18h the reaction mixture was worked up and 2.35 g of solid polymethylmethacrylate was recovered.

Best Mode for Carrying out the Invention

As presently contemplated, the best mode for carrying out the inventionis demonstrated by the fluorosilicate of Example 2B and the precedingexperiments.

Industrial Applicability

The industrial applicability of the nonhydroscopic, anionic,pentacoordinate silicates of this invention as polymerization catalystshas been demonstrated in the immediately-preceding experiments.

Although the above description includes preferred embodiments of theinvention, it is to be understood that there is no intent to limit theinvention to the precise constructions herein disclosed and that theright is reserved to all changes and modifications coming within thescope of the invention as defined in the appended claims.

I claim:
 1. Nonhygroscopic, anionic, pentacoordinate silicate of the formula ##STR12## wherein R¹ and R² are both aryl or one is aryl and the other is C₁₋₄ alkyl, or R¹ and R² taken together are ##STR13## Y is CF₃ or, when R¹ and R² are taken together, CH₃ ; X is F, CN or N₃ when Y is CF₃ ;X is F when Y is CH₃ ; M.sup.⊕ is (R³)₄ N.sup.⊕, [(R⁴)₂ N]₃ S.sup.⊕ or Cs.sup.⊕ when X is F; M.sup.⊕ is (R⁵)₄ N.sup.⊕ when X is CN; M.sup.⊕ is [(R⁴)₂ N]₃ S.sup.⊕ or (R⁵)₄ N.sup.⊕when X is N₃ ; aryl is phenyl, phenyl substituted with F or C₁₋₄ alkyl, C₁₋₄ alkoxy or naphthyl; R³ is C₁₋₄ alkyl; R⁴ is C₁₋₂ alkyl or (R⁴)₂ is --CH₂ --₅ ; and R⁵ is C₂₋₄ alkyl.
 2. Silicate of claim 1 wherein, in the formula, R¹ is methyl, R² is phenyl, X is F, Y is CF₃ and M.sup.⊕ is [(R⁴)₂ N]₃ S.sup.⊕ wherein R⁴ is methyl.
 3. Silicate of claim 1 wherein, in the formula, R¹ is methyl, R² is phenyl, X is CN, Y is CF₃ and M.sup.⊕ is (R⁵)₄ N.sup.⊕ wherein R⁵ is ethyl.
 4. Silicate of claim 1 wherein, in the formula, R¹ and R² are both phenyl, X is F, Y is CF₃ and M.sup.⊕ is [(R⁴)₂ N]₃ S.sup.⊕ wherein R⁴ is methyl.
 5. Silicate of claim 1 wherein, in the formula, R¹ and R² are both phenyl, X is CN, Y is CF₃ and M.sup.⊕ is (R⁵)₄ N.sup.⊕ wherein R⁵ is ethyl.
 6. Silicate of claim 1 wherein, in the formula, R¹ and R² are both phenyl, X is N₃, Y is CF₃ and M.sup.⊕ is [(R⁴)₂ N]₃ S.sup.⊕ wherein R⁴ is methyl.
 7. Silicate of claim 1 wherein, in the formula, R¹ and R² are taken together and are ##STR14## X is F, Y is CH₃ and M.sup.⊕ is [(R⁴)₂ N]₃ S.sup.⊕ wherein R⁴ is methyl. 